[evlatests] Antenna 12A

[Rick Perley]

    A most peculiar effect is noted in antenna 12, IF 'A':

    In the test done yesterday wherein I change bands each minute, all 
(functional) antennas return to a uniform, stable, and repeatable fringe 
level, with a single exception:  antenna 12, in IF 'A'. 

    For this antenna, at all bands *except* X, the fringe power level 
abruptly changes about 20 seconds after all others have established 
their continuity.  For most bands, this occurs about 30 to 40 seconds 
after the command to change band has occurred.  The change in effective 
power (the square of the amplitude jump) is large!

    L     8 dB down
    S      erratic, up and down.
    C     15 db up
    X     No effect (but the observation followed referenced pointing at 
X band, so I bet the effect is there)
    Q      9 dB down
    Ka    6 dB up
    K      6 dB down
    U      7 dB up

    The sequence listed above is the order in which the observations 
were made. 
    This 'effect' most likely originates in the T304's attenuators.  
It's as if 'set and remember' has been replaced for this IF with 'set, 
and readjust it later'.  As expected, the switched power tracks the 
change.